This paper continues the series of the Fornax Deep Survey (FDS). Following the previous studies dedicated to extended Fornax cluster members, we present the catalogs of compact stellar systems in the Fornax cluster as well as extended background sour
ces and point-like sources. We derive ugri photometry of ~1.7 million sources over the $sim$21 sq. degree area of FDS centered on NGC1399. For a wider area, of $sim$27 sq. degs extending in the direction of NGC1316, we provide gri data for ~3.1 million sources. To improve the morphological characterization of sources we generate multi-band image stacks by coadding the best seeing gri-band single exposures with a cut at FWHM<=0.9 arcsec. We use the multi-band stacks as detection frames. The identification of compact sources is obtained from a combination of photometric and morphometric selection criteria taking as reference the properties of sources with well-defined classification from the literature. We present a preliminary analysis of globular cluster (GC) distributions in the Fornax area. The study confirms and extends further previous results. We observe the inter-galactic population of GCs, a population of mainly blue GCs centered on NGC1399, extends over $sim$0.9Mpc, with an ellipticity $sim$0.65. Several sub-structures extend over $sim$0.5Mpc along various directions. Two of these structures do not cross any bright galaxy; one of them appears to be connected to NGC1404, a bright galaxy close to the cluster core and particularly poor of GCs. Using the gri catalogs we analyze the GC distribution over the extended FDS area, and do not find any obvious GC sub-structure bridging the two brightest cluster galaxies, NGC1316 and NGC1399. Although NGC1316 is twice brighter of NGC1399 in optical bands we estimate a factor of 3-4 richer GC population around NGC1399 compared to NGC1316, out to galactocentric distances of 40 arcmin
We describe a program to measure surface brightness fluctuation (SBF) distances to galaxies observed in the Next Generation Virgo Cluster Survey (NGVS), a photometric imaging survey covering $104~deg^2$ of the Virgo cluster in the ${u}^*,g,i,z$ bandp
asses with the Canada-France Hawaii Telescope. We describe the selection of the sample galaxies, the procedures for measuring the apparent $i$-band SBF magnitude $bar{i}$, and the calibration of the absolute $bar{M}_i$ as a function of observed stellar population properties. The multi-band NGVS data set provides multiple options for calibrating the SBF distances, and we explore various calibrations involving individual color indices as well as combinations of two different colors. Within the color range of the present sample, the two-color calibrations do not significantly improve the scatter with respect to wide-baseline, single-color calibrations involving $u^{*}$. We adopt the ${u}^*{-}z$ calibration as reference for the present galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack good ${u}^*$ photometry, we use an alternative relation based on a combination of $g{-}i$ and $g{-}z$ colors, with only a slightly larger observed scatter of 0.12 mag. The agreement of our measurements with the best existing distance estimates provides confidence that our measurements are accurate. We present a preliminary catalog of distances for 89 galaxies brighter than $B_Tapprox13.0$ mag within the survey footprint, including members of the background M and W Clouds at roughly twice the distance of the main body of the Virgo cluster. The extension of the present work to fainter and bluer galaxies is in progress.
The joint detection of gravitational waves and electromagnetic radiation from the binary neutron star (BNS) merger GW170817 has provided unprecedented insight into a wide range of physical processes: heavy element synthesis via the $r$-process; the p
roduction of relativistic ejecta; the equation of state of neutron stars and the nature of the merger remnant; the binary coalescence timescale; and a measurement of the Hubble constant via the standard siren technique. In detail, all of these results depend on the distance to the host galaxy of the merger event, NGC4993. In this paper we measure the surface brightness fluctuation (SBF) distance to NGC4993 in the F110W and F160W passbands of the Wide Field Camera 3 Infrared Channel on the Hubble Space Telescope (HST). For the preferred F110W passband we derive a distance modulus of $m{-}M=33.05pm0.08pm0.10$ mag, or a linear distance $d=40.7pm1.4pm1.9$ Mpc (random and systematic errors, respectively); a virtually identical result is obtained from the F160W data. This is the most precise distance to NGC4993 available to date. Combining our distance measurement with the corrected recession velocity of NGC4993 implies a Hubble constant $H_0=71.9pm 7.1~km~s^{-1}~Mpc^{-1}$. A comparison of our result to the GW-inferred value of $H_0$ indicates a binary orbital inclination of $i,{gtrsim},137~deg$. The SBF technique can be applied to early-type host galaxies of BNS mergers to ${sim,}100$ Mpc with HST and possibly as far as ${sim,}300$ Mpc with the James Webb Space Telescope, thereby helping to break the inherent distance-inclination degeneracy of the GW signals at distances where many future BNS mergers are likely to be detected.
We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field of NGC3115, observed as part of the VEGAS imaging survey, carried out with the VST telescope. We use deep g and i data of NGC3115, a well-studied lentic
ular galaxy with excellent scientific literature. This is fundamental to test the methodologies, verify the results, and probe the capabilities of the VEGAS-SSS. Leveraging the large field of view of the VST allow us to accurately study of the distribution and properties of SSSs as a function of galactocentric distance Rgc, well beyond ~20 galaxy effective radii, in a way not often possible. Our analysis of colors, magnitudes and sizes of SSS candidates confirms the results from existing studies, some of which carried out with 8-10m class telescopes, and further extends them to unreached Rgc distances, with similar accuracy. We find a color bimodality for the GC population and a r1/4 profile for the surface density of GCs as for the galaxy light profile. The radial color gradient of blue and red GCs previously found, for instance by the SLUGGS survey, is further extended out to the largest Rgc inspected, ~65 kpc. The surface density profiles of blue and red GCs taken separately are well approximated by a r1/4 density profile, with the fraction of blue GCs being slightly larger at larger Rgc. We do not find hints of a trend for the red GC and for the GC turnover magnitude to vary with radius, but we observe a ~0.2 mag difference in the turnover magnitude of the blue and red GCs subpopulations. Inspecting SSS sizes and colors we obtained a list of UCDs and GC candidates suitable for future spectroscopic follow-up. In conclusion, our study shows the reliability of the methodologies developed to study SSSs in the field of bright early-type galaxies, and the great potential of the VEGAS survey to produce original results on SSSs science.
The distance of NGC1316, the brightest galaxy in Fornax, is an interesting test for the cosmological distance scale. First, because Fornax is the 2nd largest cluster of galaxies at <~25 Mpc after Virgo and, in contrast to Virgo, has a small line-of-s
ight depth; and second, because NGC1316 is the galaxy with the largest number of detected SNeIa, giving the opportunity to test the consistency of SNeIa distances internally and against other indicators. We measure SBF mags in NGC1316 from ground and space-based imaging data, providing a homogeneous set of measurements over a wide wavelength interval. The SBF, coupled with empirical and theoretical calibrations, are used to estimate the distance to the galaxy. We present the first B-band SBF measurements of NGC1316 and use them together with the optical and near-IR SBF data to analyze the properties of field stars. Our distance modulus m-M=31.59 +-0.05(stat) +-0.14(sys), when placed in a consistent Cepheid distance scale, agrees with the results from other indicators. However, our result is ~17% larger than the most recent estimate based on SNeIa. Possible explanations for this disagreement are the uncertainties on internal extinction, or calibration issues. Concerning the stellar population analysis, we confirm earlier results from other indicators: the field stars in NGC1316 are dominated by a solar metallicity, intermediate age component. A substantial mismatch exists between B-band SBF models and data, a behavior that can be accounted for by an enhanced percentage of hot horizontal branch stars. Our study of the SBF distance to NGC1316, and the comparison with distances from other indicators, raises some concern about the homogeneity between the calibrations of different indicators. If not properly placed in the same reference scale, significant differences can occur, with dramatic impact on the cosmological distance ladder.
We study the two galaxies NGC4621 and NGC4374 in the Virgo cluster to derive their distances and stellar population properties. The targets have hosted three type Ia Supernova events allowing to investigate the correlations between the SNeIa and thei
r host stellar systems. Using deep BVR data, obtained with FORS2 at the VLT, we analyse the Surface Brightness Fluctuations (SBF) properties of the targets. We adopt our measurements and existing calibrations to estimate the distance of NGC4621 and NGC4374. For stellar population analysis, we measured SBF amplitudes in different galaxy regions. We present a detailed comparison between data and models to constrain the characteristics of the dominant stellar components at i) various galactic radii, and ii) in the regions where SNeIa were recorded. Our V and R SBF measures provide distances in agreement with literature estimates. The median of our and literature SBF-based distances agrees with the one from non-SBF methods. Comparing data with models we find that stellar populations properties do not change significantly along galactic radius, with a dominant population having old age and solar chemical composition. The galaxies appear similar in all properties analysed, except for B-band SBF. Since the SBF magnitudes in this band are sensitive to the properties of a hot stellar component, we speculate that such behaviour is a consequence of different diffuse hot components in the galaxies. We find that the presence of a percentage of hot-HB stars in old and metal rich stellar populations could be at the origin of the observed differences. We find a good uniformity in the V and R SBF and integrated colours in the regions where the three SNeIa exploded. On the other hand, the B-band SBF signal shows intriguing differences.
Aims.We study the photometric and structural properties of the star cluster system in the late type Sc spiral NGC 3370. Methods. BVI observations from the Advanced Camera for Surveys on board of HST are used to analyse in detail the colours, magnitud
es and spatial properties of cluster candidates. The final catalogue of sources used for the study is composed by 277 objects. Results. The colour distributions of cluster candidates appear multi-modal. Although firm age constraints need the use of more age sensitive indicators, the comparison of cluster candidate colours with the colours of Galactic and Magellanic Clouds star clusters, suggests an age difference between the various sub-peaks, with a red old sub-system, a rich population of intermediate age (~1 Gyr), and a blue tail of very young (below ~100 Myr) clusters. The luminosity functions appear normal for this type of galaxy, as for the distribution of cluster effective radii (Reff). Our analysis suggests the presence of a peak in the Reff distribution at ~3.0 pc, with blue (likely young) cluster candidates showing smaller radii respect to red (likely old) objects. Finally, inspecting the properties of candidate globular clusters, we find a colour distribution matching with Galactic Globulars, with a median [Fe/H] -1.5 dex, though a non negligible tail towards lower metallicities is also present.
We perform a series of numerical experiments to study how the nonlinear metallicity--color relations predicted by different stellar population models affect the color distributions observed in extragalactic globular cluster systems. % We present simu
lations in the $UBVRIJHK$ bandpasses based on five different sets of simple stellar population (SSP) models. The presence of photometric scatter in the colors is included as well. % We find that unimodal metallicity distributions frequently ``project into bimodal color distributions. The likelihood of this effect depends on both the mean and dispersion of the metallicity distribution, as well as of course on the SSP model used for the transformation. % Adopting the Teramo-SPoT SSP models for reference, we find that optical--to--near-IR colors should be favored with respect to other colors to avoid the bias effect in globular cluster color distributions discussed by citet{yoon06}. In particular, colors such as vh or vk are more robust against nonlinearity of the metallicity--color relation, and an observed bimodal distribution in such colors is more likely to indicate a true underlying bimodal metallicity distribution. Similar conclusions come from the simulations based on different SSP models, although we also identify exceptions to this result.
We derive Surface Brightness Fluctuations (SBF) and integrated magnitudes in the V- and I-bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total abs
olute magnitude, integrated color. We take advantage of the latter characteristic of the sample to check existing empirical calibrations of absolute SBF magnitudes both in the I- and V-passbands. Additionally, by comparing our SBF and color data with the Teramo-SPoT simple stellar population models, and other recent sets of population synthesis models, we discuss the feasibility of stellar population studies based on fluctuation magnitudes analysis. The main result of this study is that multiband optical SBF data and integrated colors can be used to significantly constrain the chemical composition of the dominant stellar system in the galaxy, but not the age in the case of systems older than 3 Gyr. SBF color gradients are also detected and analyzed. These SBF gradient data, together with other available data, point to the existence of mass dependent metallicity gradients in galaxies, with the more massive objects showing a non--negligible SBF versus color gradient. The comparison with models suggests that such gradients imply more metal rich stellar populations in the galaxies inner regions with respect to the outer ones.
